Debugger: Add missing NULL check in ReportUserInterface.

Fixes #16565.

Debugger: Rework parts of report generation.

Team:
- Adjust report generation event to include a final status code for listeners.

CliContext,TeamWindow,ReportUserinterface:
- Use aforementioned status code to indicate whether report generation
succeeded or failed.

DebugReportGenerator:
- Notify listeners if report generation fails. This may have previously
been responsible for some bug reports where it was indicated that the
debugger hung without exiting after being asked to save a report from
a crashed app.
- When dumping disassembly, retrieve it directly if necessary rather than
requesting it via the user interface listener. This also fixes the quirk
that requesting to save a crash report while looking at the source code
of a function would trigger switching it to disassembly visually.
- When walking the list of threads to dump, acquire references to all of
them before starting. Otherwise, it was potentially possible for a running
but not crashed thread to exit while we were generating the report, leaving
us with a pointer to a deleted thread. This was most likely the cause of one
of the crashes reported in #13082.
- When receiving the notification that source code state has changed, clear
the waiting function. Otherwise, it was potentially possible for us to get
other state change notifications, leading to the data semaphore being
released too often. This would then cause later potential waits such as
the stack frame memory dump to not actually wait when they should,
potentially leading them to dereference objects that weren't yet ready.
This fixes another of the crashes in #13802.

Debugger: Fix team restart request.

UserInterface:
- Add Clone() function to set of required virtuals. This asks the subclass
to create a new instance of its respective type.

{CommandLine,Graphical,Report}UserInterface:
- Implement the above function.

TeamDebugger:
- Add accessor for the currently active UI.

TargetHostInterface:
- Set correct request type when setting up the options for a team restart.
- Ask the TeamDebugger for its user interface and clone it in order to fill
in that aspect of the debug options. This fixes a regression introduced in
commit 880a64, which inadvertently resulted in team restarts no longer
working.

Debugger: Refactor non-interactive report handling.

- Add dedicated ReportDebugger application class for the case where we're
asked to do nothing more than save a report. Also add a corresponding
UserInterface subclass whose sole purpose is to take those necessary
actions and then exit.
- When the debugger is invoked via the --save-report option, we now start
via the aforementioned report/interface rather than piggybacking on the
CLI.
- Clean up CommandLineUserInterface/CliContext to remove handling for the
report saving option.

Should hopefully resolve #12155.

Debugger: Refactor non-interactive report handling.

- Add dedicated ReportDebugger application class for the case where we're
asked to do nothing more than save a report. Also add a corresponding
UserInterface subclass whose sole purpose is to take those necessary
actions and then exit.
- When the debugger is invoked via the --save-report option, we now start
via the aforementioned report/interface rather than piggybacking on the
CLI.
- Clean up CommandLineUserInterface/CliContext to remove handling for the
report saving option.

Should hopefully resolve #12155.